The properties of low-lying levels of 129Xe and 131Xe

The angular distributions and linear polarisations of gamma rays from the ( alpha ,n gamma ) reactions on 126Te and 128Te at a beam energy of 16 MeV have been measured in order to obtain information on the low-lying positive-parity levels of 129Xe and 131Xe. Spin and parity assignments of 3/2+, 5/2+, 7/2+, 7/2+ and 5/2+ have been made to levels in 129Xe at Ex=318.2, 321.7, 518.7, 665.0 and 822.1 keV respectively and of 5/2+ and 7/2+ to levels in 131Xe at 364.5 and 636.9 keV respectively. Several mixing ratios have been determined, allowing electromagnetic transition strengths to be deduced for a number of the decay transitions. The results have been discussed with reference to available calculations using the particle-vibration coupling model. This comparison has shown up a number of failures in the detailed predictions of the model. Some of these may be removed by considering the cluster structure of the particle configurations.

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